Janowicz, who was drawn into the weakest quarter of the draw that's led by No. 4 David Ferrer, rued his bad luck and missed opportunity.

"I was in really good shape," he said. "That's why I'm frickin' disappointed."

The 22-year-old Janowicz struggled to unleash his booming serve after taking pain-killing injections in the right side of his lower back before the match. The Polish No. 1 said it felt like a knife going into his lower back whenever he tried to serve. He finished with only three aces. At one point, he even tried to catch Gonzalez off guard with an underhand serve.

Gonzalez, 30, an Argentine qualifier, entered the match with a 2-9 career record on hard courts and 4-10 mark at Grand Slam tournaments. Asked if Gonzalez surprised him, Janowicz responded: "How can he surprise me when I couldn't serve? That's a stupid question. Maybe I surprised him."

Last year, Janowicz strained a leg muscle four days before the U.S. Open. He went on to lose to No. 1,098 Dennis Novikov, then a UCLA sophomore, in the first round.

"I'm so unlucky every time in New York," Janowicz said. He joked, "Maybe I'm practicing too hard for New York."

Without knowing the extent of his injury, Janowicz said he wasn't sure of his plans for the fall, which includes an important World Group Davis Cup playoff tie against Australia in Poland next month.

"I was planning after the match [to get] an MRI or X-ray," Janowicz said, "but now I don't care."

Gonzalez will play Jack Sock in the second round. Sock, a 20-year-old American, led 7-6 (2), 3-6, 5-2 when his first-round opponent, Philipp Petzschner, retired.